全文获取类型
收费全文 | 1109篇 |
免费 | 156篇 |
国内免费 | 59篇 |
专业分类
林业 | 71篇 |
农学 | 67篇 |
基础科学 | 13篇 |
89篇 | |
综合类 | 323篇 |
农作物 | 9篇 |
水产渔业 | 633篇 |
畜牧兽医 | 32篇 |
园艺 | 9篇 |
植物保护 | 78篇 |
出版年
2024年 | 1篇 |
2023年 | 26篇 |
2022年 | 39篇 |
2021年 | 43篇 |
2020年 | 62篇 |
2019年 | 49篇 |
2018年 | 52篇 |
2017年 | 53篇 |
2016年 | 60篇 |
2015年 | 51篇 |
2014年 | 46篇 |
2013年 | 80篇 |
2012年 | 53篇 |
2011年 | 82篇 |
2010年 | 70篇 |
2009年 | 49篇 |
2008年 | 68篇 |
2007年 | 69篇 |
2006年 | 69篇 |
2005年 | 56篇 |
2004年 | 56篇 |
2003年 | 41篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有1324条查询结果,搜索用时 44 毫秒
51.
Physical and biological consequences of a climate event in the central North Pacific 总被引:4,自引:0,他引:4
JEFFREY J. POLOVINA GARY T. MITCHUM NICK E. GRAHAM MITCHELL P. CRAIG EDWARD E. DEMARTINI ELIZABETH N. FLINT 《Fisheries Oceanography》1994,3(1):15-21
Climatic changes over the North Pacific which began in the mid 1970s, peaked in the early 1980s, and ended by the late 1980s, appear to have altered productivity at various trophic levels in the marine ecosystem in the central North Pacific. The climatic change resulted in increased mixed layer depth and the frequency of deep mixing events, particularly during January-March. A number of biological time series for species ranging from primary to apex levels in the North-western Hawaiian Islands, show corresponding declines in productivity of 30–50% from the early 1980s to the present. We hypothesize that during the early 1980s, increased mixing due to the climate event resulted in greater nutrient input into the euphotic zone and ultimately increased ecosystem productivity. Productivity over a range of trophic levels declined when the climate event ended. 相似文献
52.
53.
The ability to discriminate local stocks of Japanese anchovy Engraulis japonicus was assessed based on data from four elements (K, Na, P, and Sr) using an electron probe micro analyzer (EPMA) and data from
three elements (Ba, Mn, and Sr) using inductively coupled plasma mass spectrometry (ICP-MS) from the otoliths of 40 anchovy
(23.6–47.0 mm body length). Anchovy were caught at three sites (Aki-nada, Hiuchi-nada, and Osaka Bay) in the Seto Inland Sea,
and one site (Kuroshio extension) in the Pacific Ocean in 2002. In order to discriminate different spawning grounds, EPMA
data from the core portion (from core to 30 μm in the core-posterior axis) were used. Results showed that it was difficult
to discriminate between the Seto Inland Sea and the Pacific anchovy by EPMA data. Conversely, it was possible to discriminate
between the Seto Inland Sea and the Pacific anchovy by ICP-MS data from bulk otoliths. Our results showed that Mn contents
of otoliths using ICP-MS discriminate between spawning grounds most, and Ba and Sr discriminate less. The difference in elemental
compositions in anchovy otoliths between the Seto Inland Sea and the Pacific Ocean might be reflected by cumulative experienced
elemental composition of ambient sea water during life history between the Seto Inland Sea and the Pacific anchovy. 相似文献
54.
Brenda L. Norcross Evelyn D. Brown Robert J. Foy Michele Frandsen Shelton M. Gay Thomas C. Kline Doran M. Mason E. Vincent Patrick A. J. Paul Kevin D. E. Stokesbury 《Fisheries Oceanography》2001,10(Z1):42-57
Physical and biological variables affecting juvenile Pacific herring (Clupea pallasi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages‐0 and ‐1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differed among bays. The WBEC of age‐0 herring in autumn was related to over‐winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age‐0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over‐winter mortality of age‐0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age‐0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within‐bay competition. 相似文献
55.
56.
Yoshi -Nori Nakamura Masashi Ando Manabu Seoka Ken -Ichi Kawasaki Yasuyuki Tsukamasa 《Fisheries Science》2006,72(6):1140-1146
ABSTRACT: Using full-cycle cultured (FC) Pacific bluefin tuna (body length [BL], 42.6–66.4 cm; body weight [BW], 1.66–7.40 kg, n = 15), the changes in chemical compositions and histological structure of the cephalal parts of the dorsal ordinary muscles (DOM) occurring with growth were investigated. A positive correlation ( r = 0.9644, P < 0.05) was observed between BL and BW with growth. The protein, lipid and ash contents of DOM and condition factor did not change with growth. However, the glycogen content of DOM increased ( P < 0.05) from approximately 55 cm (BL) in this study. Using optical microscopic photographs, the various shapes of muscle fibers were observed and it was noted that the muscle fiber diameter increased ( P < 0.05) with growth. Using transmission electron microscopic observation, many glycogen granules were observed in muscle fibers (especially, side of connective tissue) of DOM throughout the growth stage in this study. These results indicate that the glycogen content of DOM of FC Pacific bluefin tuna increases before the lipid with growth. 相似文献
57.
58.
应用栖息地指数对印度洋大眼金枪鱼分布模式研究 总被引:10,自引:0,他引:10
运用分位数回归方法对温度、温差、氧差与印度洋大眼金枪鱼延绳钓钓获率进行二次回归分析,找出最佳上界方程,以最佳上界方程拟合的数值来建立栖息地指数(HSI)模型,从而揭示印度洋大眼金枪鱼栖息地的分布模式。研究表明,温度、温差、氧差与印度洋大眼金枪鱼延绳钓钓获率的最佳上界分位数回归方程分别为HR_(T0.9)=-44.803 7.685T_(0.9)-0.255T_(0.9)~2,HR_(dT_(0.9))=6.234 0.953dT_(0.9)-0.026dT_(0.9)~2和HR_(dO_(0.88))=7.422 4.25dO_(0.88)-0.727dO_(0.88)~2。10°N~10°S间印度洋海域大眼金抢鱼HSI指数达到0.9以上;10°N以北的波斯湾及10°S~15°S海域的HSI指数为0.8~0.9;15°S~40°S之间海域HSI指数介于0.7~0.8,其中50°E~90°E、15°S~25°S间存在一片季节性HSI指数<0.7的区域;40°S以南的海域HSI指数<0.6。 相似文献
59.
60.
Stable oxygen and carbon isotope ratios (δ18O and δ13C) from archived otoliths of Pacific halibut, Hippoglossus stenolepis, were measured to examine the most recent regime shifts in British Columbia and the Gulf of Alaska. δ18O values of these otoliths ranged from −1.5 to +2.8‰ VPDB, and were consistent with the life stages and migration behavior of halibut. δ13C varied from −3.3 to +0.9‰ VPDB, but did not show a transition from the juvenile to the adult stage as does δ18O. Evaluation of δ18O and δ13C values of mature halibut (ages 8–12) indicated that the 1977 regime shift might have a warming impact on the northeast Pacific fish stocks. In contrast, a possible regime shift around 1990 with a bottom seawater temperature decrease of about 2 °C might have occurred in both the areas. The connection between stable isotope variations in otoliths and the climate regime shifts is thus potentially useful in studying the population dynamics of Pacific halibut, and decadal scale (e.g., the last 20–30 years) ocean environmental changes. 相似文献